1. Field of the Invention
The present invention relates to a resin piston for mounting in a master cylinder in a brake system used for a vehicle and the like, for transforming brake treading force into a fluid pressure to operate a brake mechanism formed in each wheel. The invention further relates to the master cylinder, a die for molding the resin piston for the master cylinder, and a method of the manufacturing resin piston for the master cylinder.
2. Description of the Related Art
As the prior art concerning such types of resin pistons for a master cylinder, a resin piston for a master cylinder can be cited that is disclosed in Japanese Utility Model Publication No. Hei. 2-28134 and Japanese Laid-Open Patent Publication No. 2000-159088. When such a resin piston for a master cylinder is molded by injection molding, as shown in FIG. 7 of the present specification, an upper die 11 and a lower die 12, and a core for molding a concavity 13 and a core 14 are combined, and then a resin material is injected through a resin material injection hole 21 formed in the core 14. Then, after the resin material has been solidified, the core for molding a concavity 13 and the core 14 are pulled out, and the upper die 11 and the lower die 12 are removed. Thus, a resin piston for a master cylinder 1 is molded.
In the resin piston for a master cylinder 1 molded in such a way, as shown in FIG. 2, a valve mechanism 41 is fixed in a concavity 31 of the resin piston for a master cylinder 1 in a state such that a stem 42, being a part of the valve mechanism 41, is inserted into a communicating hole 32. The valve mechanism 41 opens its valve in a state such that the stem 42 is touched to a stopper pin 43 disposed in the through-hole 33 of the resin piston for a master cylinder 1, and closes the valve in a state such that the stem 42 is separated from the stopper pin 43.
In the communicating hole 32 of the resin piston for a master cylinder 1 that is molded by injection molding using the dies 11, 12 and the cores 13, 14 shown in FIG. 7, burrs are formed at a communicating section 51 in a direction to cover the communicating hole 32 along a surface at which the upper die 11 and the lower die 12 are touched with the core for molding a concavity 13. The burrs are formed because the resin material flows into small gaps between the surfaces at which the upper die 11 and the lower die 12 are touched to the core for molding a concavity 13 in the process of the molding of the resin piston for a master cylinder 1. The generation of the burrs depends on the precision of the dies, but it is very difficult to eliminate the generation of the burrs completely. Moreover, also in the case where glass fibers are mixed with the resin material with the object of increasing the strength of the resin piston for a master cylinder 1, it is difficult to eliminate generation of burrs because it is apprehended that, when the burrs are scraped off after injection molding, the resin surfaces at the places where the burrs have been scraped off become roughened and the stem 42 is caught by the roughened surfaces. Then, a problem is generated such that the stem 42 becomes unmovable because the stem 42 is caught by the burrs and then the valve mechanism 41 becomes impossible to work.
One object of the present invention is to provide a resin piston for a master cylinder capable of preventing a valve mechanism from becoming impossible to work because the stem of the valve mechanism is caught by burrs generated in the communicating hole of the resin piston for a master cylinder in the process of the injection molding thereof.
For attaining the object, a first aspect of the present invention is a resin piston for a master cylinder including a through-hole through which a stopper pin, being a component of a valve mechanism of the master cylinder, is inserted, a concavity in which the valve mechanism is fixed by being inserted therein, and a communicating hole communicating with the through-hole from the concavity, the resin piston for a master cylinder being molded by the injection of a resin material, wherein a burr to be generated by a flow of the resin material into a gap between a combined molding die and a core in a process of molding of the resin piston for a master cylinder by injection molding projects out of the communicating hole into the through-hole.
As described above, because the burr to be generated in the resin piston for a master cylinder projects out of the communicating hole, the burr does not interfere with the movement of a stem inserted into the communicating hole. According to the first aspect of the invention, operation and an effect of the resin piston for a master cylinder can be obtained such that it is prevented that the stem of the valve mechanism is caught by a burr that can be generated in the communicating hole of a resin piston for a master cylinder in the process of the injection molding to disable the valve mechanism from working.
A second aspect of the invention is a resin piston for a master cylinder including a through-hole through which a stopper pin, being a component of a valve mechanism of the master cylinder, is inserted, a concavity in which the valve mechanism is fixed by being inserted therein, and a communicating hole communicating with the through-hole from the concavity, the resin piston for a master cylinder being molded by injection of a resin material, wherein: the through-hole is molded with a core for through-hole molding; the concavity and the communicating hole are molded with a core for molding a concavity; and a part where the through-hole communicates with the communicating hole is molded in a state such that an end of the core for molding a concavity is impacted in an impact hole formed on the core for through-hole molding.
As described above, because the communicating part is molded in the state such that the end of the core for molding a concavity is impacted in an impact hole formed on the core for through-hole molding, a burr formed at the part where the communicating hole communicates with the through-hole is formed by the flow of the resin material into a gap between the end of the core for molding a concavity and the impact part. As a result, because the burr formed at the part where the communicating hole communicates with the through-hole is formed in the shape of a protrusion into the through-hole along the inner wall surface of the communicating hole, the shape of the burr does not interfere with the movement of a stem inserted in the communicating hole. According to the second aspect of the invention, operation and an effect of the resin piston for a master cylinder can be obtained such that it is prevented that the stem of the valve mechanism is caught by a burr that can be generated in the communicating hole of a resin piston for a master cylinder in the process of the injection molding to disable the valve mechanism from working.
A third aspect of the invention is the resin piston for a master cylinder as in the second aspect, wherein: the resin piston for a master cylinder is molded with a die formed by a combination of a first die and a second die, the first die including a first core, the second die including a second core; and the core for through-hole molding is constructed by a combination of the first core and the second core, whereby the impact hole is formed.
By the construction of the die for molding the resin piston for a master cylinder in such a way, it becomes possible to form the first die and the second die in a symmetrical shape. Thereby, according to the third aspect of the invention, operation and an effect of the resin piston for a master cylinder can be obtained such that the manufacture of the die is made easy in addition to the operation and the effect of the resin piston for a master cylinder of the second aspect.
A fourth aspect of the invention is the resin piston for a master cylinder as in any one of the aspects 1-3, wherein a groove is provided in a portion of an inner wall surface of said through-hole, the groove facing said communicating hole, the groove being in the shape of a flat surface oriented in a direction substantially perpendicular to the longitudinal direction in which said stopper pin is travels in operation of said master cylinder.
By the formation of such a groove in the through-hole, the surface of the through-hole becomes a flat surface nearby the impact hole which is formed in the core for through-hole molding and in which the core for molding a concavity is impacted. By the formation of the flat surface nearby the impact hole in such a way, the precision of the core for through-hole molding in the vicinity of the impact hole is easily heightened more than the case where the surface is a curved surface, and a burr generated in the vicinity of the impact hole can be made smaller than that in the case where the surface is a curved surface. Thereby, according to the fourth aspect of the invention, operation and an effect of the resin piston for a master cylinder can be obtained such that burrs can be made small in addition to the operation and the effects of the resin piston for a master cylinder as in any one of the first to the third aspects.
A fifth aspect of the invention is the resin piston for a master cylinder as in the fourth aspect, wherein the width of the groove is narrower than that of the through-hole and wider than the diameter of the stopper pin.
By the formation of the width of the groove to be narrower than that of the through-hole and wider than the diameter of the stopper pin, the position of a reciprocation end of the resin piston for a master cylinder, the reciprocation width of which is regulated by the stopper pin inserted in the through-hole while the resin piston is reciprocating, becomes easy to adjust. Thereby, according to the fifth aspect of the invention, operation and an effect of the resin piston for a master cylinder can be obtained such that the positioning of the reciprocation end of the resin piston for a master cylinder becomes easy in addition to the operation and the effects of the resin piston for a master cylinder as in the fourth aspects.
A sixth aspect of the invention is the resin piston for a master cylinder as in any one of the first to fifth aspects, wherein the through-hole includes a projecting part for preventing the stopper pin from being touched to the inner wall surface nearby a part with which the communicating hole communicates.
By the construction such that the stopper pin inserted in the through-hole is not touched to the inner wall surface nearby a part with which the communicating hole communicates, there are no possibilities that the stopper pin pushes the burrs generated at that part to bend them. Thereby, according to the sixth aspect of the invention, operation and an effect of the resin piston for a master cylinder can be obtained such that it can be prevented that the burrs that have been pushed and bent interfere with the stem of the valve mechanism inserted in the communicating hole to disable the valve mechanism from working in addition to the operation and the effects of the resin piston for a master cylinder as in any one of the first to the fifth aspects.
A seventh aspect of the invention is a resin piston for a master cylinder including a through-hole through which a stopper pin, being a component of a valve mechanism of the master cylinder, is inserted, a concavity in which the valve mechanism is fixed by being inserted therein, and a communicating hole communicating with the through-hole from the concavity, the resin piston for a master cylinder being molded by injection of a resin material, wherein: the through-hole is molded with a core for through-hole molding; the concavity and the communicating hole are molded with a core for molding a concavity; and an inner wall surface of the through-hole nearby a part where the communicating hole communicates with the through-hole is in a shape of a flat surface.
According to the resin piston for a master cylinder of the seventh aspect, the same operation and the same effect can be obtained as those of the resin piston for a master cylinder of the fourth aspect. Then, burrs can be made small regardless of the directions in which the burrs protrude.
An eighth aspect of the invention is a master cylinder equipped with the resin piston for a master cylinder as in any one of the first to the seventh aspects.
According to the master cylinder of the eighth aspect, such operation and an effect can be obtained as are brought about by the resin piston for a master cylinder as in any one of the first to the seventh aspects in the master cylinder.
A ninth aspect of the invention is a die for molding a resin piston for a master cylinder, the die molding a resin piston for a master cylinder, the resin piston for a master cylinder including a through-hole through which a stopper pin, being a component of a valve mechanism of the master cylinder, is inserted, a concavity in which the valve mechanism is fixed by being inserted therein, and a communicating hole communicating with the through-hole from the concavity, the resin piston for a master cylinder being molded by the injection of a resin material, the die comprising a core for through-hole molding for molding the through-hole and a core for molding a concavity for molding the concavity and the communicating hole, wherein a part where the through-hole communicates with the communicating hole is constructed such that the part is molded in a state in which an end of the core for molding a concavity is impacted in an impact hole formed on the core for through-hole molding.
According to the ninth aspect of the invention, the same operation and the same effect can be obtained for a master cylinder molded by the injection molding with the die for molding a resin piston for a master cylinder as those of the aforesaid resin piston for a master cylinder of the second aspect.
A tenth aspect of the invention is a method of manufacturing a resin piston for a master cylinder including a through-hole through which a stopper pin, being a component of a valve mechanism of the master cylinder, is inserted, a concavity in which the valve mechanism is fixed by being inserted therein, and a communicating hole communicating with the through-hole from the concavity, the resin piston for a master cylinder being molded by the injection of a resin material, the manufacturing method comprising the steps of: molding the through-hole with a core for through-hole molding; molding the concavity and the communicating hole with a core for molding a concavity; and molding a part where the through-hole communicates with the communicating hole in a state such that an end of the core for molding a concavity is impacted in an impact hole formed on the core for through-hole molding.
According to the tenth aspect of the invention, the same operation and the same effect can be obtained for the resin piston for a master cylinder manufactured by the manufacturing method of a resin piston for a master cylinder as those of the aforesaid resin piston for a master cylinder of the second aspect.